Colour polymorphism (variation in colour) has been hypothesized as a factor that could extend the potential niche breadth of species, allowing individuals to be phenotypically specialized to exploit specific resources and habitats while reducing overall predation through visual diversity. This phenomenon has been observed in flowers and some insects. Web-building spiders use colour for multiple purposes, such as thermoregulation and prey attraction, but the relationship between colour polymorphism and range capacity in these lineages has been poorly understood.
To examine whether colour-polymorphic web-building spiders exhibit broader ranges than monomorphic species, a recent study used GBIF-mediated data and other sources to assess 140 spider species across 58 genera. The authors conducted an extensive literature review of colour polymorphism and used geographic measures—such as range size and the number of climatic zones occupied—as proxies for species' niche breadth.
Results showed that North America, Europe and northeastern Australia had the highest numbers of reported polymorphic species. Colour-polymorphic spiders were more likely to be present on islands compared to monomorphic species, with 19 per cent of polymorphic species found exclusively in these environments. However, the authors found no overall association between colour variation and range size or niche breadth among web-building spiders.
These findings highlight the need for further research to better understand the ecological role of colour in shaping niche breadth, particularly regarding its influence on island colonization.